In recent years, because of availability of various types of compact electronic device and improvement in the radio technology, portable telephones have become very popular and are now widely used. Of the portable telephones as described above, some work on a built-in battery such as an electric battery cell, while the others work on power from such a power supply source as a cigarette lighter socket of a motor vehicle.
Also in association with popularization of portable telephones, a facsimile device which can be used in connection with the portable telephone as described above has been developed.
In the conventional type of facsimile device, however, when the facsimile device is connected to a portable telephone, if voltage of a built-in battery in the portable telephone is low, sometimes a quality of reproduced image may be deteriorated, or an error may be generated due to disconnection of the communication line, and for this reason an operator must check voltage of the built-in battery before start of use, which is troublesome to the operator.
Also in practical use, an operator sometimes starts facsimile communication without checking voltage of a built-in battery of a portable telephone, and voltage of the built-in battery in the portable telephone may drop during facsimile communication to deteriorate a quality of reproduced images or generate an error due to disconnection of the communication line, which in turn gives damages to reliability of facsimile communication. Also in the cases as described above, the operator can not always identify the cause for the error, so that the work efficiency and the operability of the facsimile device becomes worse.
Furthermore, if a conventional type of facsimile device is connected to a portable telephone receiving power from a cigarette lighter socket of a motor vehicle, also the facsimile device is placed in the motor vehicle, but as the cigarette lighter socket is used by the portable telephone, another power supply unit is required for the facsimile device, which is inconvenient in practical use.